Since 1,1,1,3,3-pentafluoropropane is available as an HFC (hydrofluoro carbon) foaming agent, a coolant or a propellant without any concern for destroying an ozone shield, and has industrial importance in view of an alternative to what is called flon gas, there is an urgent need to establish a process for producing such compound.
As a process for producing 1,1,1,3,3-pentafluoropropane, there is a known process utilizing a fluorination reaction of 1,1,1,3,3-pentachloropropane, which belongs to 1,1,1,3,3-pentahalopropane, with hydrogen fluoride. Such a fluorination reaction is generally conducted at a relatively high temperature and proceeded in a liquid phase while being supplied with an excess amount of HF with respect to 1,1,1,3,3-pentachloropropane as a raw material (or starting material). After the reaction is sufficiently proceeded, a reaction effluent (or reaction mixture) comprising unreacted HF, R-245fa as an aimed product and intermediate fluorides (such as 1,1,1,3-tetrafluoro-3-chloropropane, 1,1,1-trifluoro-3,3-dichloropropane and so on), which reaction effluent may exist in a liquid or gas state, is heated to be gasified in whole. Thus resultant material is drawn from a reactor in a gas phase, and R-245fa is obtained by subjecting the gaseous material drawn from the reactor to separation and refinement.
The fluorination reaction as described above is usually conducted in the presence of catalyst considering the yield of R-245fa. WO96/01797 discloses that Lewis acid catalyst such as antimony pentahalide can be used as the catalyst for the reaction.
It is necessary to set a reaction temperature appropriately since it is generally an important factor for determining a reaction rate as well as a scale of the reactor. As mentioned above, the fluorination reaction of 1,1,1,3,3-pentachloropropane is conducted at a relatively high temperature in order to increase the reaction rate and to gasify the reaction effluent. The gasification of the reaction effluent is required to refine the reaction effluent directly by means of a distillation apparatus which is mounted on the reactor. A temperature not less than 50° C. and generally not less than 100° C. is selected as the reaction temperature in a conventional process for producing R-245fa, though the reaction temperature may depend on a reaction pressure.
The reaction effluent from the fluorination reaction described above containing at least R-245fa and unreacted HF is drawn out from the reactor in a gas phase and subjected to the separating and refining procedure through distillation. However, it is difficult to directly separate R-245fa from the reaction effluent by a simple operation of the distillation or the like because R-245fa forms an azeotropic mixture (or azeotrope) together with HF. In order to solve this problem, Japanese Patent Kokai publication H10-17501 owned by the applicant of the present application, for example, discloses a process for separating R-245fa from a mixture of R-245fa and HF with higher efficiency by utilizing extraction.